Regular Expression Basics

PHPNW 2008Ciarán Walsh

What are regular expressions?

•Regular expressions allow matching and manipulation of textual data.

•Abbreviated as regex or regexp, or alternatively just “patterns”.

Regular Expression Basics

Literals

busMatches a ‘b’, followed by a ‘u’, followed by an ‘s’

Regular Expression Basics

Anchors

^ Matches at the beginning of a line

$ Matches at the end of a line

Regular Expression Basics

Character Classes

[abc] Matches one of ‘a’, ‘b’ or ‘c’

[a-c] Same as above (character range)

[^abc]Matches one character that is not listed

. Matches any single character

Regular Expression Basics

Alternation

a|b Matches one of ‘a’ or ‘b’

dog|cat Matches one of “dog” or “cat”

Regular Expression Basics

Quantifiers (repetition)

{x,y}Matches minimum of x and a maximum of y occurrences; either can be omitted

*Matches zero or more occurrences(any amount). Same as {0,}

+Matches one or more occurrences.Same as {1,}

?Matches zero or one occurrences.Same as {0,1}

Regular Expression Basics

Grouping

(…)

Groups the contents of the parentheses.Affects alternation and quantifiers.Allows parts of the match to be captured

for|backward “for” or “backward”(for|back)ward “forward” or “backward”

Regular Expression Basics

Delimiters

pattern / modifiers/

/i Makes match case-insensitive

Performing a Match

preg_match('/Te(.)f?/i','text',$matches);

•Returns number of matches (0 or 1)

•$matches will contain captured groups

Performing a Replacement

preg_replace('/some(text)/','\1',$text)

•Returns string after replacement

•Can use backreferences with \0-9

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(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|"(?:[^\"\r\\]|\\.|(?:(?:\r\n)?[ \t]))*"(?:(?:\r\n)?[ \t])*))*@(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\]\r\\

]|\\.)*\](?:(?:\r\n)?[ \t])*)(?:\.(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*))*|(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n

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\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|"(?:[^\"\r\\]|\\.|(?:(?:\r\n)?[ \t]))*"(?:(?:\r\n)?[ \t])*))*@(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\"

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:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|"(?:[^\"\r\\]|\\.|(?:(?:\r\n)?[ \t]))*"(?:(?:\r\n)?[ \t])*)*:(?:(?:\r\n)?[ \t])*(?:(?:(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(

?=[\["()<>@,;:\\".\[\]]))|"(?:[^\"\r\\]|\\.|(?:(?:\r\n)?[ \t]))*"(?:(?:\r\n)?[ \t])*)(?:\.(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|"(?:[^\"\r\\]|\\.|(?:(?:\r\n)?[ \t]

))*"(?:(?:\r\n)?[ \t])*))*@(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*)(?:\.(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\".\[\] \000-\031]

+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*))*|(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|"(?:[^\"\r\\]|\\.|(?:(?:\r\n)?[ \t]))*"(?:(?:

\r\n)?[ \t])*)*\<(?:(?:\r\n)?[ \t])*(?:@(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*)(?:\.(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?

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:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|"(?:[^\"\r\\]|\\.|(?:(?:\r\n)?[ \t]))*"(?:(?:\r\n)?[ \t])*)(?:\.(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|"(?:[^\"\r\\]

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,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*))*\>(?:(?:\r\n)?[ \t])*)(?:,\s*(?:(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".

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\t])*))*@(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*)(?:\.(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[

\t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*))*|(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|"(?:[^\"\r\\]|\\.|(?:(?:\r\n)?[ \t]))*"(?:(?:\r\n)?[ \t])*)*\<(

?:(?:\r\n)?[ \t])*(?:@(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*)(?:\.(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|

\Z|(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*))*(?:,@(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*)(?:\

.(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*))*)*:(?:(?:\r\n)?[ \t])*)?(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|

\Z|(?=[\["()<>@,;:\\".\[\]]))|"(?:[^\"\r\\]|\\.|(?:(?:\r\n)?[ \t]))*"(?:(?:\r\n)?[ \t])*)(?:\.(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|"(?:[^\"\r\\]|\\.|(?:(?:\r\n)?[

\t]))*"(?:(?:\r\n)?[ \t])*))*@(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\".\[\] \000-\031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*)(?:\.(?:(?:\r\n)?[ \t])*(?:[^()<>@,;:\\".\[\] \000-\

031]+(?:(?:(?:\r\n)?[ \t])+|\Z|(?=[\["()<>@,;:\\".\[\]]))|\[([^\[\]\r\\]|\\.)*\](?:(?:\r\n)?[ \t])*))*\>(?:(?:\r\n)?[ \t])*))*)?;\s*)

Don’t Use Regular Expressions!

Don’t Abuse Regular

Expressions!Some people, when confronted with a problem, think

“I know, I'll use regular expressions.”Now they have two problems. — Jamie Zawinski

Testing for a Substring

if (preg_match('/foo/', $var))

if (strpos($var, 'foo') !== false)

if (preg_match('/foo/i', $var))

if (stripos($var, 'foo') !== false)

if (preg_match('/^\d+$/', $value)) { // $value is a positive integer}

Validating an Integer

Regular Expression

•Intention is not immediately

obvious

•Not efficient

ctype (Character Type)

Validating an Integer

if (ctype_digit($value)) { // $value is a positive integer}

• Native C library (fast)

• Makes the intention obvious

$casted_value = intval($value);if ($casted_value > 0) { // $casted_value is a positive (non-zero) integer}

Validating an Integer

Casting

•Intention is fairly clear

•Casting is safe practice

•Any invalid values will result in zero

HTML Parsing

Using Regular Expressions

Using Regular Expressions

Postcodes/[A-Z]{1,2}[0-9R][0-9A-Z]? [0-9]

[A-Z]{2}/

IP Addresses @^(\d{1,2})/(\d{1,2})/(\d{4})$@

Constructing Patterns

Writing patterns is a balance between matching what you do want, against not matching what you don’t want.

preg_match('/<b><s>.+<\/s>.+<\/b>/', $html)

preg_match('@<b><s>.+</s>.+</b>@', $html)

You don’t need to use

/…/ to denote a pattern!

Greediness$html = <<<HTML <span>some text</span><span>some more text!</span>HTML;

preg_match("@<span>(.+)</span>@", $html, $matches);echo $matches[0];

preg_match("@<span>(.+?)</span>@", $html, $matches);echo $matches[0];

preg_match('`^(\w+)://(?:(.+?):(.+?)@)?(.+?)\.(\w+)$`', $s, $matches)

preg_match('` ^ (\w+):// # Protocol (?: (.+?) # Username : # : (.+?) # Password @ # @ )? # Username/password are optional (.+?) # Hostname \.(\w+) # Top-level domain $ `x', $s, $matches);

You can make your pattern readable!

preg_match('`^ (?P<protocol>\w+):// (?: (?P<user>.+?) : (?P<pass>.+?) @ )? (?P<host>.+?) \.(?P<tld>\w+) $`x', $s, $matches);

Extracting Captures

Array(    [0] => http://foo:bar@baz.example.com    [protocol] => http    [1] => http    [user] => foo    [2] => foo    [pass] => bar    [3] => bar    [host] => baz.example    [4] => baz.example    [tld] => com    [5] => com)

preg_match('`^ (?P<protocol>\w+):// (?: (?P<user>.+?) : (?P<pass>.+?) @ )? (?P<host>.+?) \.(?P<tld>\w+) $`x', $s, $matches);

if (preg_match("!>$value</(?:div|span)>!", $text))

Variable Data

$value = preg_quote($value, '!');

preg_replace('/\w+/e', 'strtoupper("\0")', 'foo bar baz')

function upper_case_match($matches) { return strtoupper($matches[0]);}preg_replace_callback('/\w+/','upper_case_match','foo bar baz')

Performing Logic on Replacements

Testing Tools

•RegexBuddy

•Reggy

•http://rubular.com

Any Questions?